Many industrial uses currently involve employing positioning members, for example for centering one element relative to another, and connecting members for fastening these elements to one another.
This applies particularly to containments used in industry, especially the nuclear industry, such as, for example, the vessels of nuclear reactors or of steam generators, or in the chemical or petrochemical industry, where a cover is fastened removably to vessel, to make it possible to carry out periodic maintenance work in the vessel.
For this purpose, the cover is fastened to the vessel by means of bolts which are screwed into internally threaded holes provided in the upper part of the vessel and which penetrate into open-ended bores provided in the flange of the cover and corresponding to the internally threaded holes.
These bolts are generally used in somewhat large numbers and relatively close to one another, and therefore the dismounting and refitting of the cover require the unscrewing and screwing of all these bolts.
These operations, particularly the screwing of the bolts, is a haphazard and difficult operation which necessitates special precautions for carrying it out.
In fact, in view of the large size and dimensions of the elements, it often happens that the coaxiality of the orifices of the two elements to be assembled together is not maintained at the moment of screwing of the bolts.
These alignment errors can cause jamming during the screwing of the bolts, thereby giving rise to stresses unevenly distributed over the moving parts and thereby to irregular and premature wear.